HID: wacom: Add support for I2C connected devices

Lenovo Thinkpad 10 has wacom digitizer connected as a I2C-HID device. Add
generic support for this.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>